It's easy to use the value of a VBScript variable in JavaScript:
document.writeln('<%= MyVBScriptVariable %>');

Or here is an example which puts the value of a VBScript variable into a JavaScript alert box:
Response.Write "<script language='JavaScript'>alert('The value is " & MyVBScriptVariable & "');</script>"

But to send the value of a JavaScript variable to VBScript, well that's another story. You could have the JavaScript fill in a hidden form field and then post the form. That way VBScript can pick up the value of the hidden form field with Request.Form("MyFieldName")